STT-MTJ is considered a promising technology for next generation non-volatile memory, as potential features include fast switching, high switching cycle endurance, low power consumption, and extended unpowered archival storage.
A conventional STT-MTJ element includes a “fixed” magnetization layer having, as its name indicates, a fixed magnetization and a “free” magnetization layer that is switchable between two mutually opposite, stable magnetization states—one being “parallel” (P) to the magnetization of the fixed layer, and the other being opposite, or anti-parallel” (AP), to the fixed magnetic layer. The electrical resistance of a given STT-MTJ element is lower when in its P state than when its AP state. The magnetization state of an STT-MTJ element can therefore be read by detecting its resistance. By assigning one of the P and AP states to represent a first binary value, e.g., a “0”, and the other to represent a second binary value, e.g., a “1” the STT-MTJ element can be a binary, i.e., one-bit storage.
The conventional STT-MTJ element, more particularly the free magnetization layer of the STT-MTJ element, can be selectively switched between the P and AP states, and visa versa, by passing an electric “write” current through its free and fixed magnetization layers. Provided the write current is above a given critical point (CPT), the STT-MTJ will switch into the P or AP state, with the selection of which states dependent on the direction of the write current. The STT-MTJ element is read by passing a “read” or “sense” current through the device, having a controlled, repeatable amplitude and, since V=IR, a sense or read voltage that is developed indicates whether the STT-MTJ element is in the P or AP state, i.e., whether the STT-MTJ element is storing a “1” or a “0.”
Needs in STT-MTJ memory include lower bit error rate, lower power, and increased storage density, e.g., bits per unit area or volume.